Glutamate is the most prominent neurotransmitter in the body, being present in over 50% of nervous tissue. Glutamate mediates its effects through two major groups of receptors: ionotropic and metabotropic. Ionotropic glutamate receptors are ion channel receptors which are often responsible for fast excitatory transmission. They are generally divided into N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainite receptors. By contrast, metabotropic glutamate receptors (mGluRs) belong to the class C G-protein-coupled receptor (GPCR) protein family and are mainly involved in the modulation of fast excitatory transmission. As such, they are attractive therapeutic targets for treatment of disorders involving malfunction of glutamate signaling. The mGluRs are further divided into three groups (Group I, II and III) based on amino acid sequence homology, signal transduction mechanism and pharmacological properties. Group I receptors includes mGluR1 and mGluR5, Group II includes mGluR2 and mGluR3 and Group III includes mGluR4, mGluR6, mGluR7 and mGluR8. The Group I mGluR1 and mGluR5 receptors couple to G-proteins of the Gq family, Gq and G11, and their activation leads to activation of phospholipase C, resulting in the hydrolysis of membrane phosphatidylinositol (4, 5)-bisphosphate to diacylglycerol, which subsequently activates protein kinase C, and inositol trisphosphate, which in turn activates the inositol trisphosphate receptor to promote the release of intracellular calcium.
Anatomical studies demonstrate a broad and selective distribution of mGluRs in the mammalian nervous system. For example, mGlu5 receptors are abundantly expressed in the striatum, cortex, hippocampus, caudate-putamen and nucleus accumbens; see for example: Shigemoto, R., Nomura, S., Hidemitsu, S., et al. Neuroscience Lett. 163, 53-57, 1993. As these brain areas have been shown to be involved in emotion, motivational processes, learning and memory, as well as motor control, mGluR5 modulators have long been regarded as possessing therapeutic potential for a wide range of indications.
mGlu5 receptor antagonists can be used for modulating the activity of the mGlu5 receptor and for use in the treatment or prevention of mGluR5 mediated disorders, such as acute and/or chronic neurological disorders, cognitive disorders and memory deficits, acute and chronic pain, protection against drug or disease induced liver damage or failure, urinary inconsistence. Other diseases contemplated include cerebral ischemia, chronic neurodegeneration including Huntington's chorea, amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, levodopa-induced dyskinesia in Parkinson's disease (PD-LID), psychiatric disorders, schizophrenia, mood disorders, emotion disorders, disorders of extrapyramidal motor function, obesity, disorders of pulmonary system and respiration, motor control and function, attention deficit disorders, concentration disorders, mental retardation (including mental retardation related to Fragile X syndrome), autism spectrum disorders (ASDs), pain disorders, neurodegenerative disorders, epilepsy, convulsive disorders, migraine, dyskinesia, eating disorders, vomiting, muscle spasms, urinary inconsistence, sleep disorders, sexual disorders, circadian disorders, drug withdrawal, drug addiction, compulsive disorders, anxiety, panic disorders, depression disorders, skin disorders, retinal ischemia, retinal degeneration, glaucoma, disorders associated with organ transplantation, asthma, ischemia and astrocytomas, diseases of the cardiovascular system, diseases of the gastrointestinal system such as gastroesophageal reflux disease (GERD) and irritable bowel syndrome, diseases of the endocrine system, diseases of the exocrine system, diseases of the skin, cancer and diseases of the ophthalmic system. The development and use of mGluR5 antagonists has been summarized in numerous review articles for example: Gasparini, F., Bilbe, G., Gomez-Mancilla, G., and Spooren, W., Current Opinion in Drug Discovery & Development. 11(5): 655-665, 2008; Rocher, J.-P., Bonnet, B., Boléa, C., et al., Current Topics in Medicinal Chemistry. 11, 680-695, 2011; Dekundy, A., Gravius, A., Hechenberger, M, et al., J. Neural Transm. 118, 1703-1716, 2011; Niswender, C. M. and Conn, P. J., Annu Rev Pharmacol Toxicol. 50, 295-322, 2010; Emmitte K A. mGlu5 negative allosteric modulators: a patent review (2010-2012). Expert Opin Ther Pat. 23(4):393-408, 2013 and Guiying Li, Morten Jørgensen and Brian M Campbell. Metabotropic glutamate receptor 5-negative allosteric modulators for the treatment of psychiatric and neurological disorders (2009-July 2013) Pharmaceutical Patent Analyst 2(6): 767-802.